The Importance Of Balanced Ventilation

24th March 2019

Mechanical Ventilation with Heat Recovery (MVHR) should be a balanced whole-house ventilation system that supplies fresh air to and extracts stale air from a building and in doing so, transfers the heat from the extracted air to the supply air via a heat exchanger.

It is important that a system be designed, installed and commissioned correctly in order to ensure a balanced system. If a system isn’t balanced correctly, it can either pressurise or depressurise the house, resulting in an inefficient system. A balanced system minimises the air leakage through the envelope of the building, by reducing the pressure differential between the inside and outside.

If the extract rate is higher than the supply rate, there will be a negative pressure in the house, resulting in cold exterior air being drawn in through the leaks in the building envelope. If the supply rate is higher than the extract rate, there will be a positive pressure, resulting in warm air being forced out through leaks in the building envelope.

A system with unbalanced airflows also has a negative effect on heat transfer between the extract & supply air. This simplistic calculation shows why.

In the colder months, when the exterior air is below freezing a system requires some form of frost protection, to prevent the heat exchanger from freezing up. The issue arises when the condensation from the extracted air gets cooled by the external freezing air, the condensate freezes and blocks the channels in the heat exchanger.

Often units protect the heat exchanger with a built-in frost protection function, which protects the heat exchanger from freezing by creating an imbalance in the airflow rates. This is done by reducing the supply of air, if this function is used for long periods, the house will get insufficient supply of air.

The Brink MVHR units have a completely new intelligent frost protection system that ensures that at low outdoor temperatures the unit’s performance remains optimal and that, if necessary, it activates the standard preheater. The preheater provides a sufficient amount of heat to the incoming air and no more, just to bring it above freezing.